Planar array optical switch and method

RELATED APPLICATION INFORMATION

This application is a continuation of U.S. patent application Ser. No. 10/781,042, entitled “Planar Array Optical Switch and Method”, filed on Feb. 18, 2004 (issued as U.S. Pat. No. 7,054,520), which is a continuation of U.S. patent application Ser. No. 10/222,750, filed on Aug. 15, 2002 (issued as U.S. Pat. No. 6,754,409), which is a continuation of U.S. patent application Ser. No. 09/326,122 entitled “Planar Array Optical Switch and Method”, filed on Jun. 4, 1999 (issued as U.S. Pat. No. 6,466,711), which claims priority from U.S. Provisional Application Ser. No. 60/088,075 entitled “Planar Array Optical Switch” filed on Jun. 5, 1998.

FIELD OF THE INVENTION

The present invention relates generally to fiber optic switches, and, more particularly, concerns a device and method for direct switching of optical signals between input and output optical fibers with minimal optical losses.

BACKGROUND OF THE INVENTION

Due to advantages over conventional electrical transmission mediums such as increased bandwidth and improved signal quality, the use of fiber optics in communications networks has become commonplace. However, as with electrical signals transmitted over wires which need to be switched between various wires in order for the signals to reach their intended destinations, optical signals similarly need to be switched between different optical fibers at appropriate junctions so that the optical signals reach their intended destinations.

One method of switching an optical signal between fibers is to convert the optical signal to an electrical signal, employ conventional electronic switching components to switch the electrical signal, and then re-convert the electrical signal to an optical signal. An alternative approach is to employ direct optical switching, wherein the optical signal is directed between fibers. The latter approach has distinct theoretical advantages, including an increase in switching speed and a reduction in signal degradation, because it eliminates the optical-to-electrical and electrical-to-optical conversions.

When implementing direct optical switching, it is desirable to have the capability to switch an optical signal from any one of a number of optical fibers entering a junction (input fibers) to any one of a number of optical fibers exiting a junction (output fibers). Several ways of achieving this have been previously proposed. One way is to bend the ends of the selected input and desired output fibers such that the two fibers point at one another (directly or via a folded optical pathway) providing a direct optical pathway for the optical signal between the fibers. The use of fixed reflectors, such as mirrors, in conjunction with bending the fiber ends has also been previously proposed. The fiber ends are not bent to point at one another, but rather are directed at one or more reflectors so that an optical signal from the input fiber is reflected to the output fiber.

SUMMARY OF THE INVENTION

One object of the present invention is to provide for direct switching of optical signals between optical fibers. The present inventor has recognized that to achieve efficient and accurate switching of the optical signal when implementing direct optical switching, it is desirable that the optical signal be directed from the input fiber such that it enters the output fiber along an optical pathway that is in substantial alignment with the output fiber. Accordingly, another object of the present invention is to provide for direct switching of optical signals between input and output optical fibers wherein the optical signal enters the output fiber along an optical pathway that is in substantial alignment with the output fiber.

The present inventor has also recognized that forming the optical signal into a focused beam, as opposed to a collimated or other diverging signal, before directing it to the output fiber with one or more reflectors is desirable in order to reduce loss of the optical signal and improve effectiveness of the switching operation. Accordingly, a further object of the present invention is to provide for direct switching of optical signals between input and output optical fibers, wherein the optical signal emitted from the input fiber is formed into a focused beam before directing it to the output fiber with one or more reflectors.

These and other objectives and advantages of the present invention are achieved by various aspects of the present invention. According to one aspect of the invention, first and second reflectors, for example mirrors, are provided wherein the first reflector is associated with the input fiber and the second reflector is associated with the output fiber. The first reflector receives the optical signal from the input fiber and is oriented so that it reflects the optical signal in a manner such that it reaches the second reflector, either directly from the first reflector or by further reflection off of other reflectors. The second reflector receives the reflected optical signal and is oriented so that the optical signal is further reflected to the output fiber along an optical pathway having an axis that is in substantial alignment with the axis of the output fiber.

In another aspect of the present invention, the first reflector does not reflect the optical signal directly to the second reflector. Rather, the optical signal from the input fiber is reflected by the first reflector to a third reflector which then reflects the optical signal to the second reflector. Further reflectors may be employed. For example, in one embodiment, the first reflector reflects the optical signal to a third reflector, which reflects the optical signal to a fourth reflector, which, in turn, reflects the optical signal to the second reflector.

In yet another aspect of the present invention, multiple reflectors are arranged into first and second arrays of reflectors, with each reflector of the first array being associated with a separate one of a plurality of input fibers and each reflector of the second array being associated with a separate one of a plurality of output fibers. The reflectors of the first and second arrays are positionable in a plurality of orientations relative to a reference orientation. For example, the reflectors of the first and second arrays may be rotatable about at least one axis of rotation to allow for positioning of the reflectors in a plurality of orientations. An optical signal may be switched between any selected one of the input fibers and any selected one of the output fibers by positioning the reflector of the first array associated with the selected input fiber in an orientation such that the optical signal is reflected, either directly or by additional reflectors, to the reflector of the second array associated with the desired output fiber. Preferably, the reflector of the second array associated with the selected output fiber is correspondingly positioned in an orientation such that the optical signal incident thereon is reflected along an optical pathway having an axis substantially aligned with the desired output fiber.

A still further aspect of the present invention involves a beam-forming unit associated with an input fiber and an associated beam-directing system for directing the beam on an optical path towards a selected output fiber. The beam forming unit associated with the input fiber receives the optical signal emitted from the end of the selected input fiber and forms it into a focused beam, as opposed to a collimated or other diverging signal. The focused beam optical signal is then directed by the beam-directing system to the selected output fiber. The output fiber is preferably associated with a lens arranged in a focused configuration relative to the beam-forming unit and the output fiber; It will thus be appreciated that a symmetric optical pathway is defined whereby an optical signal from the input fiber is made to enter the end of the output fiber. This arrangement allows for efficient bi-directional communication between the input and output fibers (the “input” and “output” labels being merely a convenience).

One more aspect of the present invention involves a method for switching optical signals between an input fiber and an output fiber. The method involves forming the optical signal into a focused beam, directing the beam towards the output fiber along an optical pathway that is, prior to the beam reaching the output fiber, substantially aligned with the output fiber, and receiving the optical signal on the end of the output fiber. A symmetrical focused beam forming unit comprised of a first focused beam forming unit and a second, substantially identical focused beam forming unit may be employed in the forming and receiving steps to enhance optical signal transmission. The step of directing may be accomplished with two active reflectors each associated with one fiber.

These and other aspects and advantages of the present invention will be apparent upon review of the following detailed description when taken in conjunction with the accompanying figures.

DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a top view illustrating a 5×5 planar array switch embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view illustrating a 9×9 matrix array switch embodiment of the present invention having two arrays of reflectors;

<figref idref="DRAWINGS">FIG. 3</figref> is a perspective view illustrating a 9×9 matrix array switch embodiment of the present invention having four arrays of reflectors;

<figref idref="DRAWINGS">FIG. 4</figref> is a top view illustrating 4×4 planar array switch embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 5</figref> is a perspective view illustrating a 16×16 matrix array switch embodiment of the present invention having two arrays of reflectors;

<figref idref="DRAWINGS">FIG. 6</figref> is a side view of the embodiment of the present invention shown in <figref idref="DRAWINGS">FIG. 5</figref>;

<figref idref="DRAWINGS">FIG. 7</figref> is a perspective view illustrating a micro electro mechanical mirror appropriate for use as a reflector in the various embodiments of the present invention;

<figref idref="DRAWINGS">FIG. 8</figref> is a side view illustrating a 4×4 matrix array switch embodiment of the present invention configured for use with one array of input and output fibers;

<figref idref="DRAWINGS">FIG. 9</figref> illustrates a collimated beam formed by a collimated beam forming unit;

<figref idref="DRAWINGS">FIG. 10</figref> illustrates a focused beam formed by a focused beam forming unit; and

<figref idref="DRAWINGS">FIG. 11</figref> illustrates a symmetrical pair of focused beam forming units in optical communication with one another;

<figref idref="DRAWINGS">FIG. 12</figref> is a cross-sectional view of a fiber illustrating the relationship between admittance and numerical aperture;

<figref idref="DRAWINGS">FIG. 13</figref> illustrates various optical parameters relevant to the present invention; and

<figref idref="DRAWINGS">FIG. 14</figref> illustrate an imaging relationship geometry in accordance with the present invention.

DETAILED DESCRIPTION

The optical switch device and method of the present invention allow for switching optical signals between optical fibers. In a communications network, the fibers entering and exiting a junction may be bundled into one group of input fibers and one group of output fibers. The ends of the input and output fibers may further be arranged into two separate rectangular arrays. However, it should be appreciated that, in communications networks, as well as in other applications, the optical fibers may be arranged in other suitable manners. For example, the ends of the input and output fibers may be mixed together in one rectangular array. Furthermore, an individual fiber may function as an input fiber as well as an output fiber depending upon the direction of propagation of the optical signal in a bi-directional communication environment. Accordingly, although the following description includes references to input and output fibers for purposes of illustration, it will be understood that each of the fibers may send and receive optical signals.

In the embodiments of the present invention discussed below individual reflectors arranged into one or more arrays of reflectors may be included. In the discussion that follows, an individual reflector of an array of reflectors will be referenced as the (i,j) reflector where i identifies the row and j the column of the specific reflector (for purposes of generality, such two-dimensional nomenclature will be used even in the case of linear arrays). Individual input and output fibers will be referenced in a like manner.

Planar Switch

Referring now to <figref idref="DRAWINGS">FIG. 1</figref>, there is illustrated one embodiment of an optical switch device <b>10</b> in accordance with the present invention. For simplicity of illustration, a linear array switch is illustrated in <figref idref="DRAWINGS">FIG. 1</figref> and more practical two-dimensional array switches will be discussed below. The optical switch device <b>10</b> is adapted to function with a linear array of five optical fibers <b>12</b> and a linear array of five optical fibers <b>14</b>. This switch device <b>10</b> is referred to as a 5×5 planar array switch because it may switch an optical signal between any one of the five fibers <b>12</b> arranged in a line (and therefore coplanar with one another) and any one of the five fibers <b>14</b> also arranged in a line. It should be appreciated that although a 5×5 planar array switch is illustrated, the present invention contemplates, in general, M×N planar array switches wherein an optical signal may be switched between any one of M fibers <b>12</b> and any one of N fibers <b>14</b> (M may equal N or they may differ).

The optical switch device <b>10</b> includes a first array <b>20</b> of five individual reflectors <b>22</b> arranged in a line and a second array <b>30</b> of five individual reflectors <b>32</b> arranged in a second line. Each of the individual reflectors <b>22</b> of the first array <b>20</b> corresponds with a separate one the fiber <b>12</b>. For example, the (1,1) reflector <b>22</b> of the first array <b>20</b> corresponds with the (1,1) fibers <b>12</b>. Likewise, each of the individual reflectors <b>32</b> of ale second array <b>30</b> correspond with a separate one of the fiber <b>14</b>. For example, the (1,1) reflector <b>32</b> of the second array <b>30</b> corresponds with the (1,1) fibers <b>14</b>.

Signals are switched by the optical switch device <b>10</b> between any one of the fiber <b>12</b> and any one of the fibers <b>14</b> in the following manner. A first optical signal (shown diagrammatically by arrow S<b>1</b>) emitted from the (1,1) fibers <b>12</b> propagates along an optical pathway <b>40</b> to the (1,1) reflector <b>22</b> of the first array <b>20</b>. To switch the first optical signal S<b>1</b> to the (1,1) fiber <b>14</b>, the (1,1) reflector <b>22</b> of the first array <b>20</b> is oriented so that first optical signal S<b>1</b> is reflected along optical pathway <b>42</b> to the (1,1) reflector <b>32</b> of the second array <b>30</b>. The (1,1) reflector <b>32</b> of the second array <b>30</b> is correspondingly oriented so that it then reflects the first optical signal S<b>1</b> along optical pathway <b>44</b> to the (1,1) fiber output <b>14</b>. It is important to note that the axis of optical pathway <b>44</b> is in substantial alignment with an axis extending centrally from the (1,1) fiber <b>14</b>. If the (1,1) reflector <b>32</b> of the second array <b>30</b> is not properly oriented, first optical signal S<b>1</b> may be reflected along any one of a number of optical pathways not in substantial alignment with the axis of the (1,1) fiber <b>14</b>, such as optical pathway <b>50</b>, impairing the switching operation. The (1,1) reflector <b>32</b> of the second array <b>30</b> could be oriented to direct an optical signal to the (1,5) fiber <b>14</b> if desired. However, such an arrangement would not provide optimal optical efficiency because the Brightness Theorem (the Second Law of Thermodynamics as applied in optics) requires that active means (e.g. the reflectors <b>32</b> of the second array <b>30</b>) be employed to condense the photons of the optical signal into a small diameter beam that fits the fiber <b>14</b> core. When fiber (1,1) in <b>12</b> is aligned to (1,1) in <b>14</b>, light may travel also from (1,1) of <b>14</b> to (1,1) of <b>12</b>.

A second optical signal (shown diagrammatically by arrow S<b>2</b>) emitted from the (1,1) fiber <b>12</b> is switched to the (1,5) fiber <b>14</b> as follows. Second optical signal S<b>2</b> propagates along optical pathway <b>40</b> to the (1,1) reflector of the first array <b>20</b> which is oriented so that second optical signal S<b>2</b> is reflected along optical pathway <b>46</b> to the (1,5) reflector of the second array <b>30</b>. The (1,5) reflector of the second array <b>30</b> is correspondingly oriented so that it then reflects second optical signal S<b>2</b> along optical pathway <b>48</b> to the (1,5) fiber <b>14</b>. As with optical pathway <b>44</b>, optical pathway <b>48</b> is substantial in alignment with an axis extending centrally from the (1,5) fiber <b>14</b>, and, in this arrangement, signals can also be communicated from (1,5) in <b>14</b> to (1,1) in <b>12</b>. It will be appreciated that illustrated pathway <b>51</b> cannot co-exist with pathway <b>52</b> as reflector (1,1) of <b>20</b> can be in only one orientation at a time. If the (1,5) reflector of the second array <b>30</b> is not oriented properly, second optical signal S<b>2</b> will be reflected along an optical pathway divergent from the axis of the (1,5) fiber <b>14</b>, such as optical pathway <b>52</b>, impairing the switching operation.

<figref idref="DRAWINGS">FIG. 4</figref> shows a 4×4 implementation of the optical switch device <b>10</b> illustrated in <figref idref="DRAWINGS">FIG. 1</figref>. The optical switch device <b>10</b> includes a base <b>16</b>. Each of the individual reflectors <b>22</b> of the first array <b>20</b> and reflectors <b>32</b> of the second array <b>30</b> are attached to the base <b>16</b>. The reflectors <b>22</b>, <b>32</b> may be rotatable about an axis of rotation perpendicular to the base <b>16</b> so that they may be oriented as necessary to switch optical signals. Each of the optical fibers <b>12</b>, <b>14</b> is associated with a separate fiber beam forming unit <b>70</b>. The fiber beam forming units <b>70</b> are comprised of an optical fiber end <b>72</b> and a lens <b>74</b> spaced apart from and coaxial with the optical fiber end <b>72</b>. Each lens <b>74</b> of the fiber beam forming units <b>70</b> associated with the fibers <b>12</b> focuses an optical signal, such as visual light or infrared radiation, emitted from the fiber end <b>72</b> of its associated fiber <b>12</b> into a beam <b>80</b> incident on the reflector <b>22</b> of the first array <b>20</b> corresponding to the associated fiber input <b>12</b>. Likewise, each lens <b>74</b> of the fiber beam forming units <b>70</b> associated with the fiber <b>14</b> receives a beam <b>80</b> from the reflector <b>32</b> of the second array <b>30</b> corresponding with the associated fiber <b>14</b> and focuses the optical signal beam <b>80</b> onto the fiber end <b>72</b> of the associated fiber <b>14</b>.

To switch an optical signal between a selected fiber <b>12</b> and a selected fiber <b>14</b>, the reflector <b>22</b> of the first array <b>20</b> corresponding with the selected fiber <b>12</b> is rotated so that the optical signal beam <b>80</b> from the lens <b>74</b> of the fibers beam forming unit <b>70</b> associated with the selected fiber <b>12</b> is reflected to the reflector <b>32</b> of the second array <b>30</b> corresponding with the selected fiber <b>14</b>. The reflector <b>32</b> of the second array <b>30</b> corresponding with the selected fiber output <b>14</b> is rotated so that it reflects the beam <b>80</b> to the lens <b>74</b> of the fiber beam forming unit <b>70</b> associated with the selected fiber <b>14</b>. As noted above, it is preferred that the beam <b>80</b> of the optical signal propagate along an optical pathway from the reflector <b>32</b> of the second array <b>30</b> to the lens <b>74</b> that is in substantial alignment with the axis of the selected fiber output <b>14</b>. Once a connection is thereby configured between a fiber <b>12</b> and a fiber <b>14</b>, two-directional communication is possible between the fibers <b>12</b> and <b>14</b>. In the description below, the fibers are sometimes designated as “input fibers” or “inputs” and “output fibers” or “outputs” for purposes of convenience, but it will be appreciated that such switch configurations support and will normally involve two-directional communication between the connected fibers.

The optical switch device <b>10</b> shown in <figref idref="DRAWINGS">FIG. 4</figref> may be implemented using micro electro mechanical (MEM) technology. The base <b>16</b> may include a circuit board or other support on which MEM chips for each of the reflector arrays <b>20</b>, <b>30</b> are mounted. The fiber inputs and outputs <b>12</b>, <b>14</b> may be positioned in V-grooves defined on the surface of the base <b>16</b>. The lenses <b>74</b> may be Frenel Zone lenses made of silicone that are defined on the surface of the base <b>16</b> and propped up to a vertical position in front of the V-grooves such that the optical axis of the each lens <b>74</b> is parallel to the surface of the base <b>16</b>. The reflectors <b>22</b>, <b>32</b> may be mirrors also made of silicone and propped up to a vertical position with the ability to rotate about an axis perpendicular to the base <b>16</b>. The optical switch device <b>10</b> should be constructed so as to maintain the optical signal beams <b>80</b> parallel to the surface of the base <b>16</b>, Small adjustments may be made to the reflectors <b>22</b>, <b>32</b> to achieve this objective.

Three-Dimensional Space Switches

As may be appreciated, the number of fiber inputs <b>12</b> and outputs <b>14</b> that can be accommodated by a planar array switch as described above is constrained by the practical limits of arranging fiber beam forming units <b>70</b> and reflectors <b>22</b>, <b>32</b> in a line. To accommodate additional input and output fibers, the present invention contemplates the utilization of three-dimensional space.

Referring now to <figref idref="DRAWINGS">FIG. 2</figref> there is shown another embodiment of the optical switch device <b>110</b> of the present invention which is adapted to function with nine fiber inputs <b>112</b> arranged in a 3×3 rectangular array and nine fiber outputs <b>114</b> arranged in a second 3×3 rectangular array. This switch device <b>110</b> is referred to as a 9×9 matrix switch because it may switch an optical signal from any one of the nine fiber inputs <b>112</b> arranged in a matrix having three rows and three columns to any one of the nine fiber outputs <b>114</b> arranged in a matrix having three rows and three columns. It should be appreciated that although a 9×9 matrix switch is illustrated the present invention contemplates, in general, M×N matrix switches wherein an optical signal may be switched from any one of M fiber inputs <b>112</b> to any one of N fiber outputs <b>114</b> (M may equal N or they may differ).

The optical switch device <b>110</b> includes a first 3×3 rectangular array <b>120</b> of individual reflectors <b>122</b> and a second 3×3 rectangular array <b>130</b> of individual reflectors <b>132</b>. Each of the individual reflectors <b>122</b> of the first array <b>120</b> corresponds with a separate one of the fiber inputs <b>112</b> and each of the reflectors <b>132</b> of the second array, corresponds with a separate one of the fiber outputs <b>114</b>. The reflectors <b>122</b>, <b>132</b> are rotatable about at least two orthogonal axes (here the x-axis and the z-axis of the reference axes illustrated) so that an optical signal may be switched from any one of the nine fiber inputs <b>112</b> to any one of the nine fiber outputs <b>114</b>. For example, an optical signal emitted from the end of the (1,1) fiber input <b>112</b> propagates along optical pathway <b>140</b> to the (1,1) reflector <b>122</b> of the first array <b>120</b>. The (1,1) reflector <b>122</b> is rotated to an orientation such that the optical signal is reflected along an optical pathway to the appropriate reflector <b>132</b> of the second array corresponding with the desired fiber output <b>114</b>. For example, depending upon its orientation, the (1,1) reflector <b>122</b> of the first array may reflect the optical signal along optical pathways <b>142</b>, <b>144</b>, <b>146</b>, <b>148</b> to the (1,1), (1,3), (3,1) or (3,3) reflectors <b>132</b>, respectively, which are correspondingly rotated to reflect the signal along optical pathways <b>150</b>, <b>152</b>, <b>154</b>, <b>156</b> to the (1,1), (1,3), (3,1) and (3,3) fiber outputs <b>114</b>, respectively. Optical pathways <b>150</b>, <b>152</b>, <b>154</b>, <b>156</b> between the second array <b>130</b> and the fiber outputs <b>114</b> are in substantial alignment with axes extending centrally from the corresponding fiber outputs <b>114</b>.

A 16×16 implementation of the optical switch device <b>110</b> illustrated in <figref idref="DRAWINGS">FIG. 2</figref> is shown in <figref idref="DRAWINGS">FIGS. 5 and 6</figref>. The first array <b>120</b> of reflectors <b>122</b> includes a first mirror holder <b>124</b>. Each of the individual reflectors <b>122</b> of the first array <b>120</b> is attached to the first mirror holder <b>124</b> and is rotatable about at least two orthogonal axes. The second array <b>130</b> of reflectors <b>132</b> includes a second mirror holder <b>134</b>. Each of the reflectors <b>132</b> of the second army <b>130</b> is attached to the second mirror holder <b>134</b> and is rotatable about at least two orthogonal axes. Each of the optical fiber inputs and outputs <b>112</b>, <b>114</b> is associated with a separate fiber beam forming unit <b>170</b>.

As shown in the side view of <figref idref="DRAWINGS">FIG. 6</figref>, the fiber beam forming units <b>170</b> are comprised of an optical fiber end <b>172</b> and a lens <b>174</b> disposed coaxial with the optical fiber end <b>172</b>. The fiber beam forming units may also include a cylindrical sleeve <b>176</b> which is fined over the fiber end <b>172</b> and lens <b>174</b>. The lens <b>174</b> may be spaced from the fiber end <b>172</b> or they may be touching, e.g., in the case of a Graded Index (GRIN) lens or a thick lens. Each lens <b>174</b> of the fiber beam forming units <b>170</b> associated with the fiber inputs <b>112</b> focuses an optical signal, such as visual light or infrared radiation, emitted from the fiber end <b>172</b> of its associated fiber input <b>112</b> into a beam <b>180</b> incident on the reflector <b>122</b> of the first array <b>120</b> corresponding to the associated fiber input <b>112</b>. Likewise, each lens <b>174</b> of the fiber beam forming units <b>170</b> associated with the fiber outputs <b>114</b> receives a beam <b>180</b> from the reflector <b>132</b> of the second array <b>130</b> corresponding with the associated fiber output <b>114</b> and focuses the optical signal beam <b>180</b> onto the fiber end <b>172</b> of the associated fiber output <b>114</b>.

To switch an optical signal between a selected fiber input <b>112</b> and a selected fiber output <b>114</b>, the reflector <b>122</b> of the first array <b>120</b> corresponding with the selected fiber input <b>112</b> is rotated so that the optical signal beam <b>180</b> from the lens <b>174</b> of the fiber beam forming unit <b>170</b> associated with the selected fiber input <b>112</b> is reflected to the reflector <b>132</b> of the second array <b>130</b> corresponding with the selected fiber output <b>114</b>. The reflector <b>132</b> of the second array <b>130</b> corresponding with the selected fiber output <b>114</b> is rotated so that it reflects the beam <b>180</b> to the lens <b>174</b> of the fiber beam forming unit <b>170</b> associated with the selected fiber output <b>114</b>. As noted above, it is important that the beam <b>180</b> of the optical signal propagate along an optical pathway from the reflector <b>132</b> of the second array <b>130</b> to the lens <b>174</b> that is in substantial alignment with the axis of the selected fiber output <b>114</b>. It is also noted that the beam <b>180</b> from the fiber <b>112</b> is aligned with the mirror <b>122</b>.

<figref idref="DRAWINGS">FIG. 7</figref> shows one of the reflectors <b>122</b>, <b>132</b> of the optical switch device <b>110</b> illustrated in <figref idref="DRAWINGS">FIGS. 2</figref>, <b>5</b> and <b>6</b>. While many different types of reflectors having appropriate reflective properties may be employed, the reflector in the illustrated embodiment is a chip mounted, micro electro mechanical (MEM) mirrors such as those manufactured by Texas Instruments. The MEM mirror <b>410</b> is constructed of silicone and is mounted on an MEM chip <b>412</b>. The mirror <b>410</b> is capable of controlled rotational movement in two degrees of freedom about two orthogonal axes <b>414</b>, <b>416</b>. The orthogonal axes <b>414</b>, <b>416</b> are parallel with the chip surface.

<figref idref="DRAWINGS">FIG. 3</figref> illustrates another embodiment of the optical switch device <b>210</b> of the present invention. As with the embodiment illustrated in <figref idref="DRAWINGS">FIG. 2</figref>, this optical switch device utilizes three-dimensional space and is also a 9×9 matrix switch for switching optical signals from any one of nine fiber inputs <b>212</b> arranged in a matrix having three rows and three columns to any one of nine fiber outputs <b>214</b> arranged in a second matrix having three rows and three columns. However, it should be appreciated that the optical switch device <b>210</b> illustrated in <figref idref="DRAWINGS">FIG. 3</figref> may generally be an M×N matrix switch.

The optical switch device <b>210</b> includes a first 3×3 rectangular array <b>220</b> of nine reflectors <b>222</b>, a second 3×3 rectangular array <b>230</b> of nine reflectors, a third 3×3 rectangular array <b>240</b> of nine reflectors <b>242</b> and a fourth 3×3 rectangular array <b>250</b> of nine reflectors <b>252</b>. Each of the reflectors <b>222</b> of the first array <b>220</b> corresponds with a separate one of the fiber inputs <b>212</b> and each of the reflectors <b>252</b> of the fourth array <b>250</b> corresponds with a separate one of the fiber outputs <b>214</b>. To allow switching of a signal from any one of the fiber inputs <b>212</b> to any one of the fiber outputs <b>214</b>, each of the reflectors <b>222</b>, <b>242</b> of the first and third arrays <b>220</b>, <b>240</b> are rotatable about an axis of rotation parallel with the z-axis of reference illustrated and each of the reflectors <b>232</b>, <b>252</b> of the second and third arrays <b>230</b>, <b>250</b> are rotatable about an axis of rotation parallel with the x-axis of reference illustrated. The reflectors <b>222</b>, <b>232</b>, <b>242</b>, <b>252</b> may be of the same type as those illustrated in <figref idref="DRAWINGS">FIG. 7</figref>, with the exception that they need only be free to rotate about one axis.

The following examples illustrate how the optical switch device <b>210</b> switches an optical signal from any one of the fiber inputs <b>212</b> to any one of the fiber outputs <b>214</b>. An optical signal from the (1,1) fiber input <b>212</b> propagates along optical pathway <b>260</b> to the (1,1) reflector <b>222</b> of the first array <b>220</b>. To switch the signal to the (1,1) fiber output <b>214</b>, the (1,1) reflector <b>222</b> of the fist array <b>220</b>, the (1,1) reflector <b>232</b> of the second array <b>230</b>, the (1,1) reflector <b>242</b> of the third array <b>240</b>, and the (1,1) reflector <b>252</b> of the fourth array <b>250</b> are each rotated to appropriate orientations such that the optical signal is reflected along optical pathways <b>262</b>, <b>272</b>, <b>282</b>, <b>292</b> from the (1,1) reflector <b>222</b> of the first array <b>220</b> to the (1,1) reflector <b>232</b> of the second array <b>230</b> to the (1,1) reflector <b>242</b> of the third array <b>240</b> to the (1,1) reflector <b>252</b> of the fourth array <b>250</b> to the (1,1) fiber output <b>214</b>. To switch the signal to the (1,3) fiber output <b>214</b>, the (1,1) reflector <b>222</b> of the first array <b>220</b>, the (1,1) reflector <b>232</b> of the second array <b>230</b>, the (1,1) reflector <b>242</b> of the third array <b>240</b>, and the (1,3) reflector <b>252</b> of the fourth array <b>250</b> are each rotated to appropriate orientations such that the optical signal is reflected along optical pathways <b>262</b>, <b>272</b>, <b>284</b>, <b>294</b> from the (1,1) reflector <b>222</b> of the first array <b>220</b> to the (1,1) reflector <b>232</b> of the second array <b>230</b> to the (1,1) reflector <b>242</b> of the third array <b>240</b> to the (1,3) reflector <b>252</b> of the fourth array <b>250</b> to the (1,3) fiber output <b>214</b>. To switch the signal to the (3,1) fiber output <b>214</b>, the (1,1) reflector <b>222</b> of the first array <b>220</b>, the (3,1) reflector <b>232</b> of the second array <b>230</b>, the (3,1) reflector <b>242</b> of the third array <b>240</b>, and the (3,1) reflector <b>252</b> of the fourth array <b>250</b> are each rotated to appropriate orientations such that the optical signal is reflected along optical pathways <b>266</b>, <b>276</b>, <b>286</b>, <b>296</b> from the (1,1) reflector <b>222</b> of the first array <b>220</b> to the (3,1) reflector <b>232</b> of the second array <b>230</b> to the (3,1) reflector <b>242</b> of the third array <b>240</b> to the (3,1) reflector <b>252</b> of the fourth array <b>250</b> to the (3,1) fiber output <b>214</b>. To switch the signal to the (3,3) fiber output <b>214</b>, the (1,1) reflector <b>222</b> of the first array <b>220</b>, the (3,1) reflector <b>232</b> of the second array <b>230</b>, the (3,1) reflector <b>242</b> of the third array <b>240</b>, and the (3,3) reflector <b>252</b> of the fourth array <b>250</b> are each rotated to appropriate orientations such that the optical signal is reflected along optical pathways <b>266</b>, <b>276</b>, <b>288</b>, <b>298</b> from the (1,1) reflector <b>222</b> of the first array <b>220</b> to the (3,1) reflector <b>232</b> of the second array <b>230</b> to the (3,1) reflector <b>242</b> of the third array <b>240</b> to the (3,3) reflector <b>252</b> of the fourth array <b>250</b> to the (3,3) fiber output <b>214</b>. It is important to note that the optical pathways <b>292</b>, <b>294</b>, <b>296</b>, <b>298</b> between the reflectors <b>252</b> of the fourth array <b>250</b> and the fiber outputs <b>214</b> are in substantial alignment with axes extending centrally from the corresponding fiber outputs <b>214</b>.

Referring now to <figref idref="DRAWINGS">FIG. 8</figref>, there is shown an additional embodiment of the optical switch device <b>310</b> of the present invention. The optical switch device <b>310</b> also utilizes three-dimensions and is adapted for switching an optical signal between any one of a number of fibers <b>312</b> and any other one of the fibers <b>312</b>, where the fibers <b>312</b> are arranged in a single array. Although a 1×4 linear array of fibers <b>312</b> is depicted, the optical switch device <b>310</b> can be adapted for use with a rectangular or other planar array of fibers <b>312</b>. It should be appreciated that each of the fibers <b>312</b> can function as a transmitting fiber and a receiving fiber depending upon the direction of propagation of the optical signal. Thus, the switch device <b>310</b> depicted in <figref idref="DRAWINGS">FIG. 8</figref> may be referred to as a 4×4 matrix array switch because it may switch an optical single from any one of four fibers <b>312</b> and to any other one of the four fibers <b>312</b>.

The optical switch device <b>310</b> includes an array <b>320</b> of rotatable reflectors <b>322</b> and a fixed reflector <b>324</b> that is fixed relative to the array <b>320</b> of rotatable reflectors <b>322</b>. Each of the rotatable reflectors <b>322</b> corresponds with a separate one of the fibers <b>312</b>. The rotatable reflectors may be of the type shown in <figref idref="DRAWINGS">FIG. 7</figref>. The optical switch device <b>310</b> also includes fiber beam forming units <b>370</b> comprised of cylindrical sleeves <b>376</b> enclosing optical fiber ends (not shown) and lenses (not shown). A separate fiber beam unit <b>370</b> is associated with each one of the fibers <b>312</b>.

An optical signal from any one of the fibers <b>312</b> is switched to any other one of the fibers <b>312</b> in the following manner. An optical signal from, for example, the (1,1) fiber <b>312</b> propagates along the optical pathway <b>330</b> between the fiber beam forming unit <b>370</b> associated with the (1,1) fiber <b>312</b> and the (1,1) rotatable reflector <b>322</b>. The (1,1) rotatable reflector <b>322</b> is rotated such the optical signal is reflected to the fixed reflector <b>324</b> along optical pathway <b>340</b>. The fixed reflector <b>324</b> reflects the optical signal along optical pathway <b>350</b> to the (1,3) rotatable reflector <b>322</b>. The (1,3) rotatable reflector <b>322</b> is rotated such that it reflects the optical signal along optical pathway <b>334</b> to fiber beam forming unit <b>370</b> associated with the (1,3) fiber <b>312</b>. Similarly, an optical signal from the (1,2) fiber <b>312</b> propagates along optical pathway <b>332</b> to the (1,2) rotatable reflector <b>322</b>, which is rotated so that the optical signal is reflected along optical pathway <b>342</b> to the fixed reflector <b>324</b>. The fixed reflector <b>324</b> reflects the optical signal along optical pathway <b>352</b> to the (1,4) rotatable reflector <b>322</b> which is rotated so that the optical signal is reflected along optical pathway <b>336</b> the fiber beam forming unit <b>370</b> associated with the (1,4) fiber <b>312</b>. The optical pathways <b>330</b>,<b>332</b>, <b>334</b>, <b>336</b> between the rotatable reflectors <b>322</b> and the fiber beam form-g units <b>370</b> associated with their corresponding fibers <b>312</b> are in substantial alignment with axes extending centrally from the corresponding fiber <b>312</b>.

Focused Beam Forming Units

As noted above, the embodiments illustrated may include a beam forming unit associated with each fiber input and output for forming optical signals into a beams. Such fiber beam forming units preferably form the optical signals into focused beams as opposed to collimated or other diverging signals.

<figref idref="DRAWINGS">FIGS. 9 and 10</figref> illustrate the differences between a collimated signal <b>510</b> formed by a collimated forming unit <b>512</b> and a focused beam <b>520</b> formed by a focused signal forming unit <b>522</b>. As shown in <figref idref="DRAWINGS">FIG. 9</figref>, a first collimated beam forming unit <b>512</b>A includes a source, such as an optical fiber end <b>514</b>, from which an optical signal, such as infrared light, is emitted and a collimating lens <b>516</b>. Since the optical fiber end <b>514</b> is not an infinitesimally small point source, rays of light from different points on the optical fiber end <b>514</b>, such as rays <b>518</b>A, <b>518</b>B, <b>518</b>C, are incident on the surface of the collimating lens <b>516</b> facing the optical fiber end <b>514</b>. The collimating lens <b>516</b> directs the rays <b>518</b>A, <b>518</b>B, <b>518</b>C such that rays from a particular point on the optical fiber end, <b>514</b> exit the lens <b>514</b> in a parallel fashion. As can be seen in <figref idref="DRAWINGS">FIG. 9</figref>, because each of the rays <b>518</b>A, <b>518</b>B, <b>518</b>C exit the lens <b>514</b> in a parallel fashion, much of the optical signal will not be incident on the lens <b>516</b> of a second fiber beam forming unit <b>512</b>B to which the optical signal is directed causing much of the optical signal to be lost.

<figref idref="DRAWINGS">FIG. 10</figref> shows a focused beam <b>520</b> formed by a first focused beam forming unit <b>522</b>A. The first focused beam forming unit <b>522</b>A includes a source, such as an optical fiber end <b>524</b>, from which an optical signal, such as infrared light, is emitted and a focused lens <b>526</b>. As with the first collimated beam forming unit <b>512</b>A, rays of light from different points on the optical fiber end <b>524</b>, such as rays <b>528</b>A, <b>528</b>B, <b>528</b>C, are incident on the surface of the focused lens <b>526</b> facing the optical fiber end <b>524</b>. Instead of directing the rays <b>528</b>A, <b>528</b>B, <b>528</b>C from each point in a parallel fashion, the focused lens <b>526</b> directs the rays <b>528</b>A, <b>528</b>B, <b>528</b>C such that the rays from a particular point on the optical fiber end <b>524</b> converge at one point on the surface of the focused lens <b>526</b> of the second focused beam forming unit <b>522</b>B to which the optical signal is directed. Thus, much of the optical signal reaches its intended destination and signal losses are minimized.

In <figref idref="DRAWINGS">FIG. 11</figref> there is shown a symmetrical system of substantially identical focused fiber beam forming units <b>522</b>A, <b>522</b>B where the fibers on each side have the same diameter of optical aperture, d, and numerical aperture N.A. Such a symmetrical system is preferred in order to facilitate optimal transmission efficiency of the optical signal between the focused fiber beam forming units <b>522</b>A, <b>522</b>B. Generally, optimum optical signal transmission efficiency is achieved when the following three equations are substantially satisfied, given certain practical constraints such as accommodating differing path lengths across the switch interface for different input fiber to output fiber switching combinations: <br /><i>D=</i>2<i>u</i>·tan(sin⁻¹(<i>N.A.</i>))+<i>d</i><br />1/<i>f=</i>1/<i>v+</i>1/<i>u</i><br /><i>d/u=D/v</i><br /> D is the effective optical aperture of the focusing lenses <b>526</b>. The distance between the lens <b>526</b> and the optical fiber end <b>524</b> of the first focused beam forming unit <b>522</b>A as well as the distance between the lens <b>526</b> and the optical fiber end <b>524</b> of the second focused beam forming unit <b>522</b>B is u. The distance between the lens <b>526</b> of the first focused beam forming unit <b>522</b>A and the lens <b>526</b> of the second focused beam forming unit <b>522</b>B is v. It will be appreciated that the value of v may vary depending on the particular switching combination under consideration and, in this regard, the focusing functionality described herein will be understood as encompassing such variations from true focusing functionality as may be desired to accommodate practical switch designs. NA is the numerical aperture of the optical fiber ends <b>524</b>, and f is the focal length of the lenses <b>526</b>. A thin lens approximation is assumed, and it is also assumed that D&gt;&gt;d. Further, if the beam carried in the optical fibers is a Gaussian beam, the effective values of d, D and NA are determined on a 1/e²irradiance basis.

Substantial Alignment

In the embodiments described above, it is noted that when the optical signal is directed to the fiber end and/or fiber beam forming unit associated with the fiber end, it will propagate along an optical pathway having an axis that is in substantial alignment with an axis extending centrally from the end of the fiber output and/or lens of the fiber beam forming unit associated with the fiber output and will pass within the effective optical aperture diameter of the beam forming unit. Those skilled in the art will appreciate that it is sufficient to have substantial alignment where the angle, if any, between the axis of the optical pathway and the axis extending from the fiber output and/or lens is substantially smaller than the N.A. of the fiber and the pathway passes through the effective optical aperture diameter of the beam forming unit.

This may be better understood by reference to <figref idref="DRAWINGS">FIGS. 12-14</figref>. <figref idref="DRAWINGS">FIG. 12</figref> is a cross sectional view of a fiber <b>600</b>. The fiber includes a core <b>602</b> for carrying optical signals surrounded by cladding <b>604</b>. In order to efficiently transmit optical signals along the length of the fiber <b>600</b>, it is desirable to provide a high degree of reflectivity at the core/cladding interface <b>606</b>, e.g., by forming the core <b>602</b> and cladding <b>604</b> from materials having differing indices of refraction or otherwise providing a reflective coating. As shown in <figref idref="DRAWINGS">FIG. 12</figref>, the illustrated interface <b>606</b> has a critical angle such that optical rays <b>608</b> having an angle of incidence less than the critical angle are transmitted through the core <b>602</b> and rays <b>610</b> having an angle of incidence greater than the critical angle are not transmitted through the core <b>602</b>. This critical angle defines the “acceptance” angle of the fiber <b>600</b>, α, the sim of which is desired as the fiber's numerical aperture.

<figref idref="DRAWINGS">FIG. 13</figref> shows the fiber <b>600</b> and lens <b>612</b> geometry. As shown, an effective optical aperture diameter, D, of the lens <b>612</b> is defined by the optical aperture diameter, d, of the fiber core <b>602</b> and the numerical aperture NA.

Specifically, as noted above: <br />D=2<i>u</i>·tan(sin⁻¹(<i>N.A.</i>))+<i>d</i><br /> Physically, this means that signals transmitted from the fiber <b>600</b> will pass within the area defined by D. Conversely, incoming optical signals that are substantially aligned with the fiber axis before entering the lens and passing within the area defined by D will be substantially accepted by the fiber <b>600</b>.

Referring to <figref idref="DRAWINGS">FIG. 14</figref>, an imaging geometry in accordance with the present invention is shown. For purposes of illustration, a straight (unfolded) optical path connecting first and second fibers is shown and the beam directing units, e.g., mirror arrays, are omitted. As described above, the first beam forming unit <b>700</b> preferably images the core <b>702</b> of first fiber <b>704</b> onto the effective diameter D₂of second beam directing unit <b>706</b>. Similarly, the second beam directing unit <b>706</b> preferably images the core <b>708</b> of second fiber <b>710</b> onto the effective diameter D₁of the first beam forming unit <b>700</b>. It will be appreciated that, in the case of an N×N switch, the length of the optical path between the beam forming units, v, may vary somewhat depending upon the particular connection. However, substantial imaging can be achieved for all connections provided that the variation of v from path to path minimized, preferably to less than about 10%. This can be achieved, for example, by increasing the magnitude of v relative to the dimension of the fiber arrays. Where folded optical paths are employed, substantial imaging can be achieved in reasonably compact switches. As shown in <figref idref="DRAWINGS">FIG. 14</figref>, the beam forming unit <b>700</b> images the core <b>702</b> onto beam forming unit <b>706</b>, and the beam forming unit <b>706</b> images the core <b>708</b> onto the beam forming unit <b>700</b>. This is graphically depicted by the arrows and inverted arrows shown in the Figure. This is accomplished by satisfying the mathematical/geometric relationships set forth above. Such imaging enhances the optical efficiency of the switch.

While various embodiments of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention will occur to those skilled in the art. However, it is expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.